QEMU implemented the configuration
VIRTIO_BALLOON_F_REPORTING && ! VIRTIO_BALLOON_F_FREE_PAGE_HINT
incorrectly: it then uses vq3 for reporting, spec says it is always 4.
This is masked by a corresponding bug in driver:
add a work around as I'm going to try and fix the driver bug.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 9a61febbd2f7..7dc3fcd56238 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -597,8 +597,23 @@ static int init_vqs(struct virtio_balloon *vb)
err = virtio_find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, vqs,
callbacks, names, NULL);
- if (err)
- return err;
+ if (err) {
+ /*
+ * Try to work around QEMU bug which since 2020 confused vq numbers
+ * when VIRTIO_BALLOON_F_REPORTING but not
+ * VIRTIO_BALLOON_F_FREE_PAGE_HINT are offered.
+ */
+ if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING) &&
+ !virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+ names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "reporting_vq";
+ callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = balloon_ack;
+ err = virtio_find_vqs(vb->vdev,
+ VIRTIO_BALLOON_VQ_REPORTING, vqs, callbacks, names, NULL);
+ }
+
+ if (err)
+ return err;
+ }
vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
--
MST
